This invention relates to an improved method for molding a unitary product comprised of multiple plastic materials.
Push buttons for the control mechanism of various electrical products and applicances, such as radios and the like, are often molded of plastic material. A desirable feature of such push buttons is the inclusion of lettering or indicia indicating the operation associated with the push button. Preferably, such lettering is colored to contrast with the color of the push button. Additionally, the push button may be lighted to accentuate the position of the button as well as the lettering on the button.
It has been suggested that a push button structure which includes the desirable feature of contrasting or lighted lettering may be fabricated from a plurality of separate plastic materials. For example, the push button itself may be made from a black plastic whereas the letters for the push button may be fabricated from a white plastic material. The button is preferably hollow and filled with clear plastic. A rod may project from the clear plastic to conduct light to the push button or to serve as a switch actuator.
Though the structure of the described push button is known, successful methods for manufacture of such structure were not available. For example, a typical difficulty encountered in the manufacture of a unitary plastic push button made from three separate plastics of distinct color is that the plastics "bleed" or intermix during molding. To overcome this problem and provide an improved method of manufacture of parts comprised of multiple plastics the present invention was developed.